A perivascular cavity may be formed along the course of a vessel to be harvested using a cannula having a transparent tapered tip. Such devices and procedures dissect tissue planes adjacent the target vessel while visualizing the vessel and connective tissue through the transparent tip via an endoscope within the cannula. Devices and procedures of these types are disclosed in the literature (See, for example, U.S. patent applications Ser. Nos. 08/593,533 and 08/502,494).
Once the perivascular cavity is formed adjacent the target vessel, it is desirable to retain the cavity in expanded condition to facilitate the surgeon's manipulation of connective tissue and lateral or branch vessels in order to liberate, "or harvest", the target vessel from the surgical site. Insufflation of the perivascular cavity using gas such as CO.sub.2 under pressure is commonly used to expand the working space within the cavity, but this procedure inhibits relatively free movement of instruments about the vessel of interest within the insufflated cavity due to the requirement for a gas-sealing port into the cavity. In contrast, mechanical retraction mechanisms are known which physically expand at least an entry portion of the cavity to facilitate direct visualization into the cavity, essentially via eye-level alignment with the separated tissue planes at the entry portion of the cavity. Simple traction mechanisms such as a stiff rod inserted into the perivascular cavity to lift up or otherwise retract the surrounding tissue away from the vessel of interest are known to be marginally useful because an additional hand may be occupied keeping adjacent tissue in tension via such retraction rod.